The invention provides a method for manufacturing an insulating layer for electro-optical devices, wherein the insulating layer contains an insulating material used for electro-optical devices and is not deteriorated in display property. The method for manufacturing an insulating layer for electro-optical devices according to the present invention can include an exposure step of performing exposure for a protrusion-forming layer containing a photosensitive resin (insulating material) with an illuminance of 80 mW/cm.sup.2 or more. The resin can be decolorized due to the exposure performed with such high illuminance, and therefore an obtained insulating material has a transmittance of 95% or more with respect to a colored ray having a wavelength of 400 nm.